Method

ABSTRACT

The present invention provides a method for inhibiting deposit formation in a fuel at a temperature of from 100 to 335° C., the method comprising combining with the fuel a composition comprising: (i) high temperature antioxidant; and (ii) a deposit inhibiting compound.

[0001] The present invention relates to a composition comprising a hightemperature antioxidant and a deposit inhibiting compound.

[0002] As discussed in U.S. Pat. No. 5,621,154, turbine combustion fueloils i.e. jet fuels, such as JP-4, JP-5, JP-7, JP-8, Jet A, Jet A-1 andJet B are ordinarily middle boiling distillates, such as kerosene orcombinations of naphtha and kerosene. Military grade JP-4, for instance,is used in military aircraft and is a blend of naphtha and kerosene.Military grades JP-7 and JP-8 are primarily highly refined kerosenes, asare Jet A and Jet A-1, which are used for commercial aircraft. Civilgrades of jet fuel are defined in ASTM D1655, DefStan 91-91, and othersimilar specifications. Such jet fuel are produced from a variety ofsources including crude oil, oil sands, oil shales, Fischer Tropschprocesses and gas to liquid processes. Refinery processing includesfuels produced by straight distillation, sometimes processed by chemicalsweetening, or hydrogen processing including hydrocracking operations,and may contain <1 to 3000 ppm sulphur.

[0003] As discussed in U.S. Pat. No. 5,468,262, the thermal stability ofjet fuel has been recognised as a problem for some years. High-speedflight necessitates that the heat generated be dissipated through thefuel i.e. the fuel is purposely preheated prior to combustion. Asaircraft have become more sophisticated with more electronic components,the heat load has increased and the fuel must be preheated to a highertemperature to absorb the energy. This makes the thermal stability ofthe fuel even more critical.

[0004] These hydrocarbon jet fuels are known to be subject todeterioration when in contact with oxygen, either on standing in air orduring pre-combustion heating. Such deterioration is thought to be dueto the presence in the fuel of constituents which undergo oxidativechanges resulting in the formation of non-volatile resinous substances.In addition, the high temperatures and oxygen-rich atmospheres inaircraft and engine fuel system components encourage the degradation ofthe fuel resulting in particulate and deposit formation.

[0005] The resinous substances and other deposits plug up the componentsleading to operational problems including reduced thrust and performanceanomalies in the augmentor, poor spray patterns and premature failure ofmainburner combustors and problems with fuel controls. Further, theengine exhaust becomes smoky and sooty and engine noise increases, bothof which are undesirable characteristics for jet engines.

[0006] The problems of deposition from fuels at elevated temperatures isnot limited to the use of fuels in the extreme environments encounteredin aviation. As discussed in WO-A-99/25793 in some oil fired devices,such as boilers and slow heating cookers, e.g. of the Aga™ type,kerosene oil fuel is passed down a narrow metal feed pipe to thecombustion chamber where it is burnt. Parts of the pipe are sufficientlynear the hot chamber for them to be heated to significant temperatures,resulting in the risk of thermal degradation of the fuel in the pipe,especially with slow feed rates and high residence times in the pipe.This degradation can form solid deposits which reduce the flow andultimately stop it, causing the combustion to stop. To overcome thismanufacturers of such devices have for many years recommended to theirusers that at least once each six months such pipe parts are cleaned ofsolid deposits of coke or other materials.

[0007] GB 2261441 teaches a fuel composition in the gasoline boilingrange containing a polyoxyalkylene compound and the reaction product ofa polyamine and a hydrocarbyl succinic acylating agent.

[0008] U.S. Pat. No. 5,601,624 discloses a fuel composition comprising afuel and a minor amount of a multifunctional additive such as adispersant, corrosion inhibitor or antioxidant. The additive is thereaction product of an oxygenated amine with a dicarbonyl compound and ahydrocarbyl or hydrocarbylene amine. e.g. a polyetheramine, glyoxal anda succinimide.

[0009] U.S. Pat. No. 5,990,056 relates to a lubricant compositioncomprising an organo substituted benzophenone and at least oneco-additive such as a lubricant antioxidant, a lubricant dispersant, oran antiwear additive. The compound is thought to act as a lubricant baseor blend stock, a solubility enhancer or a deposit reducing agent.

[0010] GB 923190 teaches a synergistic antioxidant mix for use inorganic material. The mix comprises a phosphite ester and a methylenebis phenol. The use in jet fuel, kerosene, and fuel oil is disclosed.

[0011] GB 791526 discloses dimethyl-(phenyl)-phosphates (e.g.dimethyl-(tolyl)-phosphate).

[0012] Use of the compounds in hydrocarbons in the gasoline boilingrange is taught.

[0013] In order to alleviate some of the problems outlined above andmeet certain performance and storage requirements, fuels including jetfuels often contain additives such as antioxidants, deposit inhibitingcompounds, metal deactivators, corrosion inhibitors and lubricityimprovers. It would be apparent to one skilled in the art thatsynergistic combinations of any of these additives would be desirable.

[0014] Antioxidant additives are used not only in fuel but also in arange of other substances such as lubricants, plastics and foodproducts.

[0015] The present invention alleviates the problems of the prior art.

[0016] The present invention relates to the provision of combinations,in particular synergistic combinations, of antioxidants and depositinhibiting compounds.

[0017] Aspects of the invention are defined in the appended claims.

[0018] In one aspect the present invention provides a method forinhibiting deposit formation in a fuel at a temperature of from 100 to335° C., the method comprising combining with the fuel a compositioncomprising: (i) high temperature antioxidant; and (ii) a depositinhibiting compound.

[0019] By the term “high temperature antioxidant” it is meant anantioxidant which may prevent oxidation in a fuel at high temperature.In particular it is meant an antioxidant which provides improvedantioxidant performance when measured in accordance with the HighTemperature Antioxidant Protocol below.

[0020] In one aspect the present invention provides a compositioncomprising (i) a phosphorus-containing antioxidant; and (ii) a depositinhibiting compound

[0021] In one aspect the present invention provides a fuel compositioncomprising (a) a fuel (b) a composition as defined herein.

[0022] In one aspect the present invention provides a use of acomposition as defined herein for

[0023] (i) the inhibition of oxidation of a fuel composition comprisingthe composition and a fuel; and/or

[0024] (ii) the inhibition of deposit formation in a fuel compositioncomprising the composition and a fuel; and/or

[0025] (iii) the inhibition of particle formation from the oxidationproduct(s) of a fuel; and/or

[0026] (iv) the solubilisation of deposits and/or deposit precursors.

[0027] In one aspect the present invention provides a compositioncomprising (i) a phosphorus-containing antioxidant; and (ii) a depositinhibiting compound, in an amount or a ratio to produce an antioxidantand/or deposit inhibitory synergistic effect.

[0028] We have found that the combination of a phosphorus-containingantioxidant, such as di-dodecyl hydrogen phosphonate, and a depositinhibiting compound, such as 2300 ButA Mannich, act in fuels to inhibitoxidation and/or deposition of material from fuels at elevatedtemperatures. The oxidation products or deposited material may blockfilters and reduce the efficiency of an engine in which the fuel iscombusted. We have surprisingly found that the combination of productswhich form the present composition act in a synergistic manner toprevent or inhibit oxidation and/or deposition of material.

[0029] We have found that by the provision of the compositions of thepresent invention an anti-oxidant and/or deposit inhibitory effect maybe observed, for example by study using Hot Liquid Process Simulator(HLPS). The anti-oxidant and/or deposit inhibitory effect is greaterthan one would expect from the anti-oxidant and/or deposit inhibitoryeffect of each of the composition components, i.e. the combination ofcomponents provides a synergistic effect.

[0030] Preferred Aspects

[0031] Antioxidant

[0032] As discussed above in one aspect the present invention provides amethod for inhibiting deposit formation in a fuel at a temperature offrom 100 to 335° C., the method comprising combining with the fuel acomposition comprising: (i) high temperature antioxidant; and (ii) adeposit inhibiting compound.

[0033] Preferably the high temperature antioxidant of the presentinvention is a phosphorus-containing antioxidant.

[0034] Preferably the phosphorus-containing antioxidant is anorganophosphorus-containing antioxidant.

[0035] By the term “organophosphorus-containing anti-oxidant” it ismeant a compound comprising at least P and C and may optionally compriseone or more other suitable atoms. Examples of such atoms may includehydrogen, sulphur and oxygen.

[0036] By the term “organophosphorus-containing anti-oxidant” it ismeant a compound containing a C—P bond and/or a C—O—P bond and/or aC—S—P bond.

[0037] Preferably the phosphorus-containing antioxidant is or is derivedfrom an organophosphorus acid. Preferably the organophosphorus acid isselected from phosphorus acid, phosphonous acid, phosphinous acid,phosphoric acid, phosphonic acid or phosphinic acid.

[0038] In one preferred aspect the phosphorus-containing antioxidant isor is derived from an ester of an organophosphorus acid. Preferably theorganophosphorus acid is selected from phosphorus acid, phosphonousacid, phosphinous acid, phosphoric acid, phosphonic acid or phosphinicacid.

[0039] In a preferred aspect the phosphorus-containing antioxidant is anester of an organophosphorus acid. More preferably thephosphorus-containing antioxidant is an ester of an organophosphorusacid selected from phosphorus acid, phosphonous acid, phosphinous acid,phosphoric acid, phosphonic acid or phosphinic acid.

[0040] In a highly preferred aspect the phosphorus-containingantioxidant is or is an ester of a phosphonic acid.

[0041] In a highly preferred aspect the phosphorus-containingantioxidant is an ester of a phosphonic acid.

[0042] Preferably the phosphorus-containing antioxidant contains atrivalent or pentavalent phosphorus.

[0043] Preferably the phosphorus-containing antioxidant is a compound ofFormula l:

[0044] wherein R¹, R² and R³ are independently selected from H andhydrocarbyl; and X, Y, and Z are independently selected from O and S.

[0045] Preferably the phosphorus-containing antioxidant is a compound ofFormula II:

[0046] wherein R¹, R² and R³ are independently selected from H andhydrocarbyl; and X, Y, and Z are independently selected from O and S.

[0047] In the present specification by the term “hydrocarbyl group” itis meant a group comprising at least C and H and may optionally compriseone or more other suitable substituents. Examples of such substituentsmay include halo-, alkoxy-, nitro-, a hydrocarbon group, an N-acylgroup, a cyclic group etc. In addition to the possibility of thesubstituents being a cyclic group, a combination of substituents mayform a cyclic group. If the hydrocarbyl group comprises more than one Cthen those carbons need not necessarily be linked to each other. Forexample, at least two of the carbons may be linked via a suitableelement or group. Thus, the hydrocarbyl group may contain hetero atoms.Suitable hetero atoms will be apparent to those skilled in the art andinclude, for instance, sulphur, nitrogen and oxygen.

[0048] In one preferred embodiment of the present invention, thehydrocarbyl group is a hydrocarbon group.

[0049] Here the term “hydrocarbon” means any one of an alkyl group, analkenyl group, an alkynyl group, an acyl group, which groups may belinear, branched or cyclic, or an aryl group. The term hydrocarbon alsoincludes those groups but wherein they have been optionally substituted.If the hydrocarbon is a branched structure having substituent(s)thereon, then the substitution may be on either the hydrocarbon backboneor on the branch; alternatively the substitutions may be on thehydrocarbon backbone and on the branch.

[0050] X, Y and Z

[0051] Preferably at least one of X, Y or Z is O.

[0052] Preferably at least one of Y and Z is O.

[0053] Preferably X is S or O, Y is O and Z is O. Thus in a highlypreferred aspect the antioxidant of the present invention is of theformula

[0054] wherein X, R¹, R² and R³ are as defined above.

[0055] Preferably each of X, Y and Z is O. Thus in a highly preferredaspect the antioxidant of the present invention is of the formula

[0056] wherein R¹, R² and R³ are as defined above.

[0057] In one aspect at least one of X, Y or Z is O and wherein at leastone of X, Y or Z is S.

[0058] In one aspect, preferably when the antioxidant is of formula I Xis S. Thus in this aspect the antioxidant of the present invention is ofthe formula

[0059] wherein Y, Z, R¹, R² and R³ are as defined above.

[0060] R¹, R² and R³

[0061] As disclosed above R¹, R² and R³ are independently selected fromH and hydrocarbyl.

[0062] Preferably R¹ is selected from H and hydrocarbon.

[0063] Preferably R¹ is selected from H and C₁₋₃₀ hydrocarbyl, such asC₁₋₂₀ hydrocarbyl, C₁₋₁₅ hydrocarbyl, C₁₋₁₀ hydrocarbyl, C₁, C₂, C₃, orC₄ hydrocarbyl.

[0064] Preferably R¹ is selected from H and C₁₋₃₀ hydrocarbon, such asC₁₋₂₀ hydrocarbon, C₁₋₁₅ hydrocarbon, C₁₋₁₀ hydrocarbon, C₁, C₂, C₃, orC₄ hydrocarbon.

[0065] Preferably R¹ is selected from H and C₁₋₃₀ alkyl, such as C₁₋₂₀alkyl, C₁₋₁₅ alkyl, C₁₋₁₀ alkyl, C₁, C₂, C₃, or C₄ alkyl.

[0066] Preferably R¹ is selected from H and C₁₋₁₀ alkyl, for example C₁,C₂, C₃, or C₄ alkyl.

[0067] In a highly preferred aspect R¹ is H.

[0068] In some aspects, for example when the compound is formula II, R¹is selected from

[0069] H and C₁₋₁₀₀ hydrocarbyl, such as C₁₋₅₀ hydrocarbyl, C₁₋₃₀hydrocarbyl, C₁₋₂₅ hydrocarbyl, C₁₋₂₀ hydrocarbyl, C₁₋₁₅ hydrocarbyl,C₁₋₁₂ hydrocarbyl, C₅₋₂₅ hydrocarbyl, C₈₋₂₀ hydrocarbyl, C₁₀₋₁₅hydrocarbyl, C₁₀, C₁₁, C₁₂, C₁₃, or C₁₄ hydrocarbyl.

[0070] H and C₁₋₁₀₀ hydrocarbon, such as C₁₋₅₀ hydrocarbon, C₁₋₃₀hydrocarbon, C₁₋₂₅ hydrocarbon, C₁₋₂₀ hydrocarbon, C₁₋₁₅ hydrocarbon,C₁₋₁₂ hydrocarbon, C₅₋₂₅ hydrocarbon, C₈₋₂₀ hydrocarbon, C₁₀₋₁₅hydrocarbon, C₁₀, C₁₁, C₁₂, C₁₃, or C₁₄ hydrocarbon.

[0071] H and C₁₋₁₀₀ alkyl, such as C₁₋₅₀ alkyl, C₁₋₃₀ alkyl, C₁₋₂₅alkyl, C₁₋₂₀ alkyl, C₁₋₁₅ alkyl, C₁₋₁₂ alkyl, C₅₋₂₅ alkyl, C₈₋₂₀ alkyl,C₁₀₋₁₅ alkyl, C₁₀, C₁₁, C₁₂, C₁₃, or C₁₄ alkyl.

[0072] H and C₁₋₁₀₀ straight chain alkyl, such as C₁₋₅₀ alkyl, C₁₋₃₀alkyl, C₁₋₂₅ alkyl, C₁₋₂₀ alkyl, C₁₋₁₅ alkyl, C₁₋₁₂ alkyl, C₅₋₂₅ alkyl,C₈₋₂₀ alkyl, C₁₀₋₁₅ alkyl, C₁₀, C₁₁, C₁₂, C₁₃, or C₁₄ alkyl.

[0073] In a preferred aspect R² and R³ are independently selected from Hand hydrocarbon groups.

[0074] Preferably R² and R³ are independently selected from H and C₁₋₁₀₀hydrocarbyl, such as C₁₋₅₀ hydrocarbyl, C₁₋₃₀ hydrocarbyl, C₁₋₂₅hydrocarbyl, C₁₋₂₀ hydrocarbyl, C₁₋₁₅ hydrocarbyl, C₁₋₁₂ hydrocarbyl,C₅₋₂₅ hydrocarbyl, C₈₋₂₀ hydrocarbyl, C₁₀₋₁₅ hydrocarbyl, C₁₀, C₁₁, C₁₂,C₁₃, or C₁₄ hydrocarbyl.

[0075] Preferably R² and R³ are independently selected from H and C₁₋₁₀₀hydrocarbon, such as C₁₋₅₀ hydrocarbon, C₁₋₃₀ hydrocarbon, C₁₋₂₅hydrocarbon, C₁₋₂₀ hydrocarbon, C₁₋₁₅ hydrocarbon, C₁₋₁₂ hydrocarbon,C₅₋₂₅ hydrocarbon, C₈₋₂₀ hydrocarbon, C₁₀₋₁₅ hydrocarbon, C₁₀, C₁₁, C₁₂,C₁₃, or C₁₄ hydrocarbon.

[0076] Preferably R² and R³ are independently selected from H and C₁₋₁₀₀alkyl, such as C₁₋₅₀ alkyl, C₁₋₃₀ alkyl, C₁₋₂₅ alkyl, C₁₋₂₀ alkyl, C₁₋₁₅alkyl, C₁₋₁₂ alkyl, C₅₋₂₅ alkyl, C₈₋₂₀ alkyl, C₁₀₋₁₅ alkyl, C₁₀, C₁₁,C₁₂, C₁₃, or C₁₄ alkyl.

[0077] Preferably R² and R³ are independently selected from H and C₁₋₁₀₀straight chain alkyl, such as C₁₋₅₀ alkyl, C₁₋₃₀ alkyl, C₁₋₂₅ alkyl,C₁₋₂₀ alkyl, C₁₋₁₅ alkyl, C₁₋₁₂ alkyl, C₅₋₂₅ alkyl, C₈₋₂₀ alkyl, C₁₀₋₁₅alkyl, C₁₀, C₁₁, C₁₂, C₁₃, or C₁₄ alkyl.

[0078] In a highly preferred aspect the antioxidant is of the formula

[0079] wherein n and m are independently selected from 1 to 15,preferably 5 to 15, preferably 7 to 13, preferably 8 to 12, preferably9, 10 or 11.

[0080] In a highly preferred aspect the antioxidant is of the formula

[0081] This compound is commonly known as di-dodecyl hydrogenphosphonate.

[0082] In a highly preferred aspect the antioxidant is of the formula

[0083] This compound is commonly known as tridodecylphosphite.

[0084] Deposit Inhibiting Compound

[0085] Preferably the deposit inhibiting compound is of Formula II

Polymer-Q-R   (II)

[0086] wherein Polymer is a polymeric hydrocarbyl group; wherein Q is anoptional ring system; and wherein R is a group selected from H andhydrocarbyl.

[0087] R

[0088] In one aspect if R is a hydrocarbyl group it is free of acarboxylic acid group (—COOH).

[0089] In one aspect if R is a hydrocarbyl group it is free of ahydroxyl group (—OH).

[0090] In one aspect R is selected from H and a nitrogenous hydrocarbylgroup.

[0091] In one aspect R is a nitrogenous hydrocarbyl group.

[0092] The term “nitrogenous hydrocarbyl group” as used herein means agroup comprising at least C, H and N and may optionally comprise one ormore other suitable substituents. Examples of such substituents mayinclude halo-, alkoxy-, an alkyl group, a cyclic group etc. In additionto the possibility of the substituents being a cyclic group, acombination of substituents may form a cyclic group. If the nitrogenoushydrocarbyl group comprises more than one C then those carbons need notnecessarily be linked to each other. For example, at least two of thecarbons may be linked via a suitable element or group. Thus, thenitrogenous hydrocarbyl group may contain hetero atoms. Suitable heteroatoms will be apparent to those skilled in the art and include, forinstance, sulphur.

[0093] In one preferred embodiment of the present invention, thenitrogenous hydrocarbyl group is a nitrogenous hydrocarbon group.

[0094] Here the term “nitrogenous hydrocarbon group” means a groupcontaining only C, H and N (with the proviso of course that Q togetherwith R contains no greater than 2 nitrogen) including primary, secondaryand tertiary amines, which group may be linear, branched or cyclic. Theterm nitrogenous hydrocarbon group also includes groups which have beenoptionally substituted. If the nitrogenous hydrocarbon group is abranched structure having substituent(s) thereon, then the substitutionmay be on either the hydrocarbon backbone or on the branch;alternatively the substitutions may be on the hydrocarbon backbone andon the branch.

[0095] Preferably the combined total of nitrogen and carbon atoms in thenitrogenous hydrocarbon group is from 1 to 10, preferably from 2 to 8,preferably 2 to 6, for example 2, 4 or 6. Preferably in this aspect thenitrogenous hydrocarbon group is a straight chain.

[0096] Q

[0097] Q is an optional ring system. In one aspect the optional ringsystem Q is present.

[0098] In one aspect Q is substituted. Preferably Q is substituted withone or more groups selected from ═O and —OH.

[0099] In one preferred aspect Q is an aromatic ring.

[0100] In one preferred aspect Q has 4 to 10 members, preferably 4 to 6members, preferably 5 or 6 members.

[0101] Q may be heterocyclic ring or may contain only carbon. The ringmay be a hydrocarbyl ring. In the present specification by the term“hydrocarbyl ring” it is meant a cyclic group comprising at least C andH and may optionally comprise one or more other suitable ring members.Suitable ring members will be apparent to those skilled in the art andinclude, for instance, sulphur, and nitrogen.

[0102] In one preferred aspect Q is a carbon ring or a heterocyclic ringcontaining carbon and one nitrogen.

[0103] In one aspect Q is selected from a ring system of the formula

[0104] wherein A is C or N and n is an integer from 1 to 5. In thisaspect preferably Q is selected from a ring system of the formula

[0105] wherein A is C or N, i.e. n is 1 or 2.

[0106] In one aspect Q contains an imide group, namely a group of theformula

[0107] Preferably Q is a ring system of the formula

[0108] In one aspect Q is a hydrocarbon ring substituted with at leastone alcohol group. The hydrocarbon ring may be aromatic and in apreferred aspect is a six membered aromatic ring. Preferably Q is a ringsystem of the formula

[0109] In one aspect Q together with R is a Mannich group or is derivedfrom or derivable from a Mannich reaction.

[0110] When the ring Q contains a nitrogen, preferably group R isattached to ring Q via the nitrogen. In other words, the nitrogen ofgroup Q may be substituted by group R.

[0111] R & Q

[0112] In one aspect Q together with R contains no greater than 2nitrogens.

[0113] In one aspect when Q together with R contains 2 nitrogens each ofthe nitrogens is a member of a heterocyclic ring.

[0114] In one aspect Q together with R contains only 2 nitrogens andwherein each of the nitrogens is a member of a heterocyclic ring.

[0115] In one aspect Q together with R contains no greater than 1nitrogen.

[0116] In one aspect Q together with R contains no greater than 1 basicnitrogen.

[0117] Polymer

[0118] Preferably Polymer is a hydrocarbyl group having from 10 to 200carbons.

[0119] Preferably Polymer is a branched or straight chain alkyl group,preferably a branched alkyl group.

[0120] Preferably Polymer has a molecular weight of from 700 to 2500,preferably 1000 to 2300, preferably approximately 1000 or approximately2300.

[0121] Preferably Polymer is polyisobutene (PIB). Conventional PIBs andso-called “high-reactivity” PIBs (see for example EP 0565285) aresuitable for use in the invention. High reactivity in this context isdefined as a PIB wherein at least 50%, preferably 70% or more, of theterminal olefinic double bonds are of the vinylidene type.

[0122] Preferably Polymer is polyisobutene having a molecular weight offrom 700 to 2500, preferably 1000 to 2300, preferably approximately 1000or approximately 2300.

[0123] In a highly preferred aspect the deposit inhibiting compound isselected from compounds of the formulae

[0124] wherein PIB is polyisobutene.

[0125] In a highly preferred aspect the deposit inhibiting compound isselected from compounds of the formulae

[0126] wherein PIB is polyisobutene having a molecular weight ofapproximately 2300

[0127] wherein PIB is polyisobutene having a molecular weight ofapproximately 1000

[0128] 1000 ButA PIBamine

[0129] wherein PIB is polyisobutene having a molecular weight ofapproximately 1000

[0130] 1000 ButA PIBSI

[0131] Composition

[0132] In a preferred aspect the deposit inhibiting compound is providedin the composition to provide a fuel treat rate of 1-500 mg/l activeconcentration, preferably 50-300 mg/l, preferably 50-150 mg/l,preferably 75-125 mg/l, preferably approximately 100 mg/l.

[0133] In a preferred aspect the antioxidant is provided in thecomposition to provide a fuel treat rate of 1-100 mg/l activeconcentration, preferably 5-80 mg/l, preferably 5-50 mg/l preferably5-20 mg/l , preferably 7-15 mg/l, preferably 10-13 mg/l.

[0134] In a preferred aspect the composition further comprises a metaldeactivator. Preferably the metal deactivator is N,N′-disalicylidene1,2-propanediamine or N,N′-disalicylidene 1,2-cyclohexyldiamine.

[0135] In a preferred aspect the metal deactivator is provided in thecomposition to provide a fuel treat rate of 1-50 mg/l activeconcentration, preferably 1-30 mg/l, preferably 1-20 mg/l, preferably1-10 mg/l, preferably 1-5 mg/l, preferably approximately 2 mg/l.

[0136] In a preferred aspect the composition further comprises a furtherantioxidant. A possible further antioxidant is BHT(2,6-di-t-butyl-4-methyl phenol) or other aviation approved hinderedphenol antioxidants. The additional antioxidants may be added in orderto protect fuel from the build up peroxides on storage. In a preferredaspect the further antioxidant is provided in the composition to providea fuel treat rate 0-100 mg/l, preferably 5-80 mg/l, preferably 10-50mg/l, preferably 10-30 mg/l, preferably approximately 25 mg/l.

[0137] Fuel Composition

[0138] In one aspect the present invention provides a fuel compositioncomprising (a) a fuel (b) a composition comprising (i) aphosphorus-containing antioxidant; and (ii) a deposit inhibitingcompound

[0139] Preferably the fuel is an aviation turbine fuel.

[0140] Preferably the fuel is JP-8 aviation fuel.

[0141] The deposit inhibiting compound may be present in the compositionin amount of at least 1 mg/l or at least 5 mg/l, such as 1 to 1000, 5 to1000 for example 5 to 500, 5 to 200 or 10 to 100 mg/l active ingredientbased on the weight of the composition e.g. the fuel composition. Theadditive may be mixed with the jet or other fuel composition in the formof a concentrate in solution, e.g. in an aliphatic aromatic hydrocarbonin 20-80% w/w solution, or it may be added as such to give a solution inthe fuel.

[0142] The composition can comprise jet fuel. The composition cancomprise kerosene, in particular in jet fuel. The main component of thejet fuel itself is usually a middle boiling distillate boiling point inthe range 150-300° C. at atmospheric pressure and the fuel is usuallykerosene which may be mixed with gasoline (naphtha) and optionally lightpetroleum distillate as in mixtures of gasoline and kerosene. The jetfuel may comprise mixtures of gasoline and light petroleum distillate,e.g. in weight amounts of 20-80:80-20 such as 50-75:50-25 which weightamounts may also be used for mixtures of gasoline and kerosene. The jetfuels for military use are designated JP-4 to 8 e.g. JP-4 as 65%gasoline/35% light petroleum distillate (according to US Mil. Spec. (MIL5624G)), JP-5, similar to JP-4 but of higher flash point, JP-7, a highflash point special kerosene for advanced supersonic aircraft and JP-8,a kerosene similar to Jet AI (according to MIL 83133C). Jet fuel forcivilian use is usually a kerosene type fuel and designated Jet A or JetAI. The jet fuel may have a boiling point of 66-343° C. or 66-316° C.(150-650° F. e.g. 150-600° F.), initial boiling point of 149-221° C.,e.g. 204 C. (300-430° F., e.g. 400° F.), a 50% boiling point of 221-316°C. (430-600° F.) and a 90% boiling point of 260-343° C. (500-650° F.)and API Gravity of 30-40. Jet fuel for turbojet use may boil at 93-260°C. (200-500° F.) (ASTM D1655-006). Further details on aviation fuels maybe obtained from “Handbook of Aviation Fuel Properties”, Co-ordinatingResearch Council Inc., CRC Report No. 530 (Society of AutomotiveEngineers Inc., Warrendale, Pa., USA, 1983) and on US military fuels,from “Military Specification for Aviation Turbine Fuels”, MIL-T-5624P.

[0143] The jet fuel may be the straight run kerosene optionally withadded gasoline (naphtha), but frequently has been purified to reduce itscontent of components contributing to or encouraging formation ofcoloured products and/or precipitates.

[0144] Among such components are aromatics, olefins, mercaptans, phenolsand various nitrogen compounds. Thus the fuels may be purified to reducetheir mercaptan content e.g. Merox fuels and copper sweetened fuels orto reduce their sulphur content e.g. hydrogen treated fuels or Merifinedfuels. Merox fuels are made by oxidation of the mercaptans and have alow mercaptan S content (e.g. less than 0.005% wt S) such as0.0001-0.005% but a higher disulphide S content (e.g. at most 0.4% or atmost 0.3% wt S such as 0.05-0.25 e.g. 0.1-2%); their aromatic (e.g.phenolics) and olefins content are hardly changed. Hydrogen processedjet fuels are ones in which the original fuel has been hydrogenated toremove at least some of sulphur compounds e.g. thiols and under severeconditions to saturate the aromatics and olefins; hydrofined jet fuelshave very low sulphur contents (e.g. less than 0.01% S by weight).Merifined fuels are fuels that have been extracted with an organicextractant to reduce or remove their contents of sulphur compoundsand/or phenols. The jet fuel may also contain metals, either followingcontact with metal pipes or carried over from the crude oil, oil sands,shale oil or sources; examples of such metals are copper, nickel, ironand chromium usually in amounts of less than 1 ppm e.g. each in 10-150ppb amounts. Merox, straight run and hydrogen processed are preferredand may be used in JP- 4-8 jet fuels.

[0145] The fuel comprising kerosene may also be a fuel for combustionespecially for non motive purposes, e.g. power generation, steamgeneration, and heating, especially for use in buildings and forcooking, e.g. as described above. The fuel is particularly suitable forthe devices e.g. boilers and slow cookers as described above in whichthere is localised preheating of the fuel before it is combusted.

[0146] Such fuels are known as burning kerosene and may have the samephysical properties as the kerosene based jet fuels described above,e.g. straight run kerosene, or kerosene modified to reduce its contentof at least one of aromatics, olefins and sulphur compounds, asdescribed above. The fuel may also contain metals as described above.

[0147] The fuel compositions of the invention contains the depositinhibiting compound and may also contain at least one conventionaladditive e.g. for jet fuels or burning fuels such as an antioxidant,corrosion inhibitor, lubricity improvers, metal deactivators (MDA), leakdetection additives, “special purpose” additives such as drag reducingagents, anti-icing additives and static dissipaters such as Stadis®,especially in amounts each of 1-2000 ppm.

[0148] The use or method of the present invention is typically performedwhen the fuel or fuel composition is at a temperature of no greater than1100° F. The fuel or fuel composition is typically at a temperature of325 to 425° F. during use. In a one aspect the use or method of thepresent invention is preferably performed when the fuel or fuelcomposition is at a temperature of from 100 to 335° C.

[0149] The present invention will now be described in further detail byway of example only with reference to the accompanying figures inwhich:—

[0150]FIG. 1 shows HLPS apparatus.

[0151] The present invention will now be described in further detail inthe following examples.

EXAMPLES

[0152] The additives discussed below were tested for HLPS data. TheProtocol for this test is given below.

HLPS Protocol

[0153] Scope—HLPS is a self-contained testing apparatus designed to testthe thermal properties of base and additised jet fuels. The testinvolves the flow of the test fuel over a heated test surface (@335° C.)under high pressure (500 psi).

[0154] Summary—The HLPS is run in accordance with ASTM D-3241. Theconditions for testing are set to those used by the USAF in extensivethermal stability programmes.

[0155] The basic principles of the HLPS are shown in FIG. 1. As shown inFIG. 1, 1 litre of test fuel is pressurised in a stainless steelreservoir to 500 psi. The fuel is then pumped via a pre-filter over aheated test section (@335° C.). As deposition occurs on both the tubeand in the fuel bulk the bulk deposit is measured as a filter dropchange across a 17 micron filter. A pressure transducer cell measuresthe rate of pressure drop (in mmHg min-1). Finally the spent fuel isreturned to the top of the reservoir, separated by an appropriate seal.

[0156] Apparatus—Alcor HLPS—is a modular version of the equipment set upas defined in ASTM D-3241. The test section must be of stainless steel316 and free from grease. The filter to be used must be of 17 micronmesh as supplied by Alcor.

[0157] Materials

[0158] Base fuels—are fuels free of additives

[0159] Main Test Procedure

[0160] Sample Preparation

[0161] 1. Filter 1 litre of base test fuel through a 0.7 micron filter.

[0162] 2. If fuel is to be additised transfer the known weight ofadditive(s) to a 1 litre volumetric flask using base test fuel.

[0163] 3. Transfer the test fuel to a 2 litre beaker. Aerate using theglass bubbler attachment for a minimum of 6 minutes. Test run must beinitiated within 1 hour of aeration.

[0164] 4. Transfer the test fuel to the stainless steel reservoir.

[0165] 5. Check the piston seal for degradation. If OK place the pistonhead on the surface of the fuel and push down using the supplied handleuntil fuel begins to seep up from the reservoir.

[0166] 6. Place the large ‘O’ ring seal in the reservoir top and secureto the top of the reservoir using a socket wrench.

[0167] 7. Connect the connector tube from the filter unit to the testcell using new ‘O’ ring.

[0168] 8. Connect all remaining pipe-work using new ‘O’ rings.

[0169] Main Test Run Procedure.

[0170] 1. Close BLEED valve on front of HLPS and open PRESSURISE valve.Ensure that system is pressurised to 500 psi.

[0171] 2. Ensure that lower knob on delta P cell is turned to BYPASS andupper knob is VENT CLOSED.

[0172] 3. Switch on PUMP. Red indicator light will come on. Ensure thatFUEL FLOW CONTROL is set to 230. This equates to a flow rate of 3mls/min.

[0173] 4. Allow fuel to pump round system until a steady drop rate isseen through the Perspex window on top of the fuel reservoir. Whensteady count the time taken for 20 drops. If the time is 9 seconds±1seconds this is acceptable for 3 mls/min.

[0174] 5. Ensure that HEATER TUBE TEMP. CONTROL is set to 335 deg. C.Switch on HEATER. Red indicator light will come on. Needle will thenrise to the vertical. Heater power is controlled by using the POWERCONTROL dial. A typical setting for this procedure is 82±10 volts.

[0175] 6. Switch on the differential pressure module (DPM) by depressingthe POWER button.

[0176] 7. When needle reads correct temperature switch the delta P lowerknob to RUN. This will divert the fuel flow through the differentialpressure cell.

[0177] 8. Allow the pressure read out on the differential pressuremodule to equilibrate and press RECORD. The differential pressure willbe recorded every 5 minutes on the in-built printer.

[0178] 9. Allow the test to run whilst monitoring the differentialpressure change. The DPM has an alarm setting that will causemulti-point printing at 125 mmHg. If the differential pressure risesabove 300 mmHg turn the lower DPM knob to bypass and note the time.

[0179] 10. In all cases allow the test run to complete a 5 hour testsequence. The HLPS will shut down automatically after 5 hours.

[0180] Analysis—Analysis is carried out on the Leco Carbon AnalyserRC412.

[0181] Results—Are quoted for 2 readings.

[0182] Filter blockage—Record the change in differential pressure duringthe run. Results are quoted in mmHg min-1, e.g. 300/45, 0/300. The firstfigure is the change in differential pressure in mmHg the latter thetime in minutes

[0183] Carbon deposit weight—Record the value in μgcm⁻²

High Temperature Antioxidant Protocol

[0184] A high temperature antioxidant candidate is formulated in acomposition comprising the high temperature antioxidant candidate, 2300ButA Mannich (a deposit inhibiting compound) and N,N′-disalicylidene1,2-propanediamine (an MDA). The composition is dosed into at leastthree test fuels at a treat rate for each fuel of

[0185] (i) 100 mg 2300 ButA Mannich per litre of fuel;

[0186] (ii) 0.032 mmoles high temperature antioxidant candidate perlitre of fuel; and

[0187] (iii) 2 mg N,N′-disalicylidene 1,2-propanediamine per litre offuel

[0188] Each dosed fuel is subjected to HPLS testing in accordance withthe above Protocol.

[0189] The currently approved stabiliser package SpecAid 8Q462(available from Shell Aviation as AeroShell Performance Additive 101) isdosed into the same base fuels at a treat rate 256 mg/l for each fuel.Each dosed fuel is subjected to HPLS testing in accordance with theabove Protocol.

[0190] The pressure drop of each fuel containing the candidate and thepressure drop of each fuel containing SpecAid 8Q462 is recorded.

[0191] The pressure drop recorded for the candidate composition in agiven fuel is compared to pressure drop recorded for SpecAid 8Q462 inthe same fuel. A candidate is considered to “pass” if for each fuel thepressure drop recorded for the candidate composition is no greater than2 mmHg more than the pressure drop recorded for SpecAid 8Q462.

[0192] The carbon deposit weight of each fuel containing the candidatecomposition and the carbon deposit weight of each fuel containingSpecAid 8Q462 is recorded. The carbon deposit weight for the candidatecomposition is averaged across the number of fuels tested. The carbondeposit weight for SpecAid 8Q462 is averaged across the number of fuelstested. A candidate is considered to “pass” if the average carbondeposit weight for the candidate composition is less than, equal to orno greater than 10 mg more than the average carbon deposit weight forthe SpecAid 8Q462.

[0193] A candidate which “passes” in respect of both pressure drop andcarbon deposit weight constitutes a “high temperature antioxidant”within the scope of the present invention.

[0194] The at least three test fuels may be selected from Shell HT, POSF3684 (USAF B), Phillips HT, Sunoco, Shell Merox, USAF A, BP Air Merox,Marathon HT, and Phillips Merox. In one aspect of this protocol thecandidate composition is dosed into POSF 3684 (USAF B), Phillips HT,Sunoco, Shell Merox, USAF A, BP Air Merox, and Phillips Merox. In oneaspect of this protocol the candidate composition is dosed into ShellHT, POSF 3684 (USAF B), Phillips HT, Sunoco, Shell Merox, USAF A, BP AirMerox, Marathon HT, and Phillips Merox.

[0195] Syntheses

[0196] PIBSIs

[0197] 1000/Butylamine PIBSI

[0198] 1000 mwt high reactive PIB derived PIBSA (467.6 g) was stirredwith Shellsol AB (311.8 g) in a 1 l oil jacketed reactor equipped withan overhead stirrer, thermometer and Dean & Stark trap. Whilst still atroom temperature butylamine (31.5 g) was added in one aliquot withcontinued stirring. An immediate exotherm was noted. The reaction mixwas heated to ˜150° C. for three hours whilst removing water. 720 g ofproduct was isolated.

[0199] Analysis of the product showed it to contain 40% m/m solvent,0.81% m/m nitrogen.

[0200] 1000 ButA PlBamine

[0201] PIB chloride (153 g, chlorine content 4.89% m/m) was placed in astirred reactor with butylamine (61.6 g) and Shellsol (50 ml. Thereactor contents were heated to reflux for 19.5 hours. Crystalline solidcould be seen in the solution as the reaction proceeded. The reactionwas allowed to cool and an excess of aqueous sodium carbonate was mixedwith the reactor contents. After separation the organics were washedwith water and dried over sodium sulphate. The unreacted butylamine wasremoved under reduced pressure leaving the 190 g product plus solvent.

[0202] Analysis of the product showed it to contain 23% m/m solvent,0.95% m/m nitrogen, 1% m/m residual chlorine.

[0203] Mannich Compounds

[0204] The Mannichs for use in the present invention may be synthesisedin accordance with the teaching of EP 0831141.

[0205] Results

[0206] The following data were obtained.

[0207] HLPS testing was performed and data collected. Results given aresurface carbon deposit weight (μgcm⁻²) and filter blockage, ΔP,(mmHg/min). A result of 0/300 means that no blockage has occurred overthe 300 minutes of the test, a result of 300/101 means that the filterhas completely blocked in 101 minutes.

[0208] The following antioxidants/antioxidant compositions were used inthe Examples AO1 2,6-di-t-butyl-4-methyl phenol AO2Octadecyl-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl) propionate AO3 Methylenebis (dibutylthiocarbamate) AO4 2,2′thiodiethylbis-(3,5-di-t-butyl-4-hydroxyphenyl) propionate AO5 commerciallyavailable alkylated phenol AO63,5-bis-(1,1-dimethyl-ethyl)-4-hydroxybenzenepropanoic ester of C₁₄₋₁₅alcohol AO7 “synergistic blend of an aminic and a phenolic antioxidant”AO8 di-dodecyl hydrogen phosphonate AO9 SpecAid 8Q462 AO10 dioleylhydrogenophosphite AO11 tridodecylphosphite AO12 trinonylphenylphosphiteAO13 di-n-octylphosphite AO14 isodecyl diphenylphosphite AO15 butylatedtriphenyl phosphorothioate AO16ethyl-3-((bis(1-methylethoxy)phosphinothionyl)thio)propionate AO17ascorbyl palmitate AO18 tocopherol

Example 1

[0209] Assessment of Different Antioxidants in Two Fuels

[0210] A number of different antioxidants/antioxidant compositions wereassessed in two basefuels in a package containing a ButA Mannichdetergent and a MDA. The results were compared against the fuel, MDA anddetergent alone or in various combinations. The HLPS data are givenbelow. Shell HT POSF 3684 (USAF B) Carbon Carbon Composition μgcm⁻² ΔPμgcm⁻² ΔP Basefuel 39 300/230 125 300/45  Basefuel + detergent 38  0/30090.5  12/300 Basefuel + MDA 62  0/300 24 300/101 Basefuel, detergent +MDA 39  0/300 29.5  5/300 Basefuel, detergent, MDA + AO1 (25 mg/l) 41.5 0/300 27  0/300 Basefuel, detergent, MDA + AO2 (60.3 mg/l) 18  0/300 32 1/300 Basefuel, detergent, MDA + AO3 (50 mg/l) 66  0/300 32  4/300Basefuel, detergent, MDA + AO4 (45 mg/l) 60  0/300 34  0/300 Basefuel,detergent, MDA + AO5 (25 mg/l) 19 300/270 19  9/300 Basefuel, detergent,MDA + AO6 (60 mg/l) 47  6/300 32  6/300 Basefuel, detergent, MDA + AO7(50 mg/l) 40.3  4/300 28.4 300/26  Basefuel, detergent, MDA + AO8 (13.7mg/l) 6  0/300 7  0/300 Basefuel, detergent, MDA + AO8 (5 mg/l) 26 0/300 — — Basefuel, detergent, MDA, AO8 (5 mg/l) + AO1 15  1/300 — —(25 m/l) Basefuel, detergent, MDA, AO8 (5 mg/l) + AO2 23  0/300 — — (60mg/l) Basefuel, detergent, MDA, AO8 (13.7 mg/l) + 13  0/300 — — AO2 (60mg/l) Basefuel + AO9 (256 mg/l) 10  0/300 19  0/300 Basefuel, detergent,MDA + AO10 (21 mg/l) 8  0/300 17  4/300 Basefuel, detergent, MDA + AO11(18.8 mg/l) 5  0/300 19  1/300 Basefuel, detergent, MDA + AO12 (12 mg/l)12  0/300 66  13/300 Basefuel, detergent, MDA + AO13 (10 mg/l) 9  0/30016  13/300 Basefuel, detergent, MDA + AO14 (12 mg/l) 52  0/300 17  2/300Basefuel, detergent, MDA + AO15 (12 mg/l) 68  0/300 22  0/300 Basefuel,detergent, MDA + AO16 (9 mg/l) 11  0/300 22  3/300 Basefuel, detergent,MDA + AO17 (10 mg/l*) 42  0/300 — — Basefuel, detergent, MDA + AO18(13.8 mg/l) 48  0/300 — —

[0211] In at least one the fuels and in some instances in both fuels,the addition of a phosphorus containing antioxidant to a package alreadycontaining detergent and MDA decreases the amount of carbon depositingon the surface of the HLPS tube and/or decreases filter blockage. Thetraditional antioxidant (BHT—AO1) tested does not show this effect.

Example 2

[0212] Assessment of Different Detergents in combination with PreferredAntioxidant

[0213] The preferred anti-oxidant of Example 1, namely AO8, was combinedwith three different detergents. The results were compared against thefuel, MDA, detergent and anti-oxidant alone or in various combinations.The HLPS data are given below. Shell HT Carbon Composition μgcm⁻² ΔPBasefuel 39 300/230 Basefuel + detergent A 38  0/300 Basefuel + A08alone (10 86.5  3/300 mg/l) Basefuel + MDA 62  0/300 Basefuel, detergentA + 25  0/300 AO8 Basefuel, detergent A + 39  0/300 MDA Basefuel,detergent A, 13  0/300 MDA + AO8 Basefuel, detergent B, 23  0/300 MDA +AO8 Basefuel, detergent C, 12  0/300 MDA + AO8

[0214] Each of the full packages gives better performance than eachcomponent individually at the treat rate used in the package.

Example 3

[0215] Assessment of Package in Different Fuels

[0216] HLPS results for package based on AO8 in different fuels. Forcomparison the HPLS results for basefuel and SpecAid 8Q462 at a treatrate 256 mg/l are also given. ΔP Carbon Carbon Carbon ΔP Spec- ΔP BaseSpecAid Package Fuel Base Aid Package μgcm⁻² μgcm⁻² μgcm⁻² Shell HT300/230 0/300 0/300 39 10 13 POSF 3684 300/45  0/300 2/300 125 19 17USAF B Phillips  1/300 0/300 0/300 31 25 3 HT Sunoco  0/300 0/300 0/30051 35 10.6 Shell 300/170 3/300 0.8/300   157 46 24 Merox USAF A 300/1480/300 0/300 95 31 9 BP Air  3/300 0/300 0/300 44 33 13 Merox Marathon 4/300 1/300 0/300 55 9 15 HT Phillips 300/27  1/300 0/300 26 46 20Merox

[0217] In all the fuels tested there is a large decrease in both bulkand surface carbon deposits when using the above additive package.

[0218] All publications mentioned in the above specification are hereinincorporated by reference. Various modifications and variations of thedescribed methods and system of the invention will be apparent to thoseskilled in the art without departing from the scope and spirit of theinvention. Although the invention has been described in connection withspecific preferred embodiments, it should be understood that theinvention as claimed should not be unduly limited to such specificembodiments. Indeed, various modifications of the described modes forcarrying out the invention which are obvious to those skilled inchemistry or related fields are intended to be within the scope of thefollowing claims

1. A method for inhibiting deposit formation in a fuel at a temperatureof from 100 to 335° C., the method comprising combining with the fuel acomposition comprising: (i) high temperature antioxidant; and (ii) adeposit inhibiting compound
 2. A method according to claim 1 wherein thehigh temperature antioxidant is a phosphorus-containing antioxidant. 3.A composition comprising: (i) a phosphorus-containing antioxidant; and(ii) a deposit inhibiting compound
 4. The invention according to claim 2or 3 wherein the phosphorus-containing antioxidant is anorganophosphorus-containing antioxidant.
 5. The invention according toclaim 2, 3 or 4 wherein the phosphorus-containing antioxidant is or isderived from an organophosphorus acid.
 6. The invention according to anyone of claims 2 to 5 wherein the phosphorus-containing antioxidant is oris derived from an ester of an organophosphorus acid.
 7. The inventionaccording to any one of claims 2 to 6 wherein the organophosphorus acidis selected from phosphorus acid, phosphonous acid, phosphinous acid,phosphoric acid, phosphonic acid or phosphinic acid.
 8. The inventionaccording to claim 7 wherein the phosphorus-containing antioxidant is anester of organophosphorus acid selected from phosphorus acid,phosphonous acid, phosphinous acid, phosphoric acid, phosphonic acid orphosphinic acid.
 9. The invention according to claim 8 wherein thephosphorus-containing antioxidant is an ester of a phosphonic acid. 10.The invention according to any one of claims 2 to 9 wherein thephosphorus-containing antioxidant is a compound of Formula I or II:

wherein R¹, R² and R³ are independently selected from H and hydrocarbyl;and X, Y, and Z are independently selected from O and S.
 11. Theinvention according to claim 10 wherein at least one of X, Y or Z is O.12. The invention according to claim 8 or 9 wherein at least one of Yand Z is O.
 13. The invention according to claim 10, 11 or 12 wherein Xis S or O, Y is O and Z is O.
 14. The invention according to any one ofclaims 10 to 13 wherein each of X, Y and Z is O.
 15. The inventionaccording to claim 10 or 11 wherein at least one of X, Y or Z is O andwherein at least one of X, Y or Z is S.
 16. The invention according toany one of claims 10 to 15 wherein R¹ is selected from H andhydrocarbon.
 17. The invention according to any one of claims 10 to 16wherein R¹ is selected from H and C1-15 alkyl.
 18. The inventionaccording to any one of claims 10 to 17 wherein R¹ is H.
 19. Theinvention according to any one of claims 10 to 18 wherein R² and R³ areindependently selected from H and hydrocarbon groups having from 1 to 50carbons.
 20. The invention according to claim 19 wherein R² and R³ areindependently selected from H and hydrocarbon groups having from 1 to 25carbons.
 21. The invention according to claim 19 wherein R² and R³ areindependently selected from H and straight chain alkyl groups havingfrom 1 to 25 carbons.
 22. The invention according to claim 19 wherein R²and R³ are independently straight chain alkyl groups having from 10 to15 carbons.
 23. The invention according to any one of claims 2 to 22wherein the phosphorus-containing antioxidant is a compound of Formulal:

wherein R¹, R² and R³ are independently selected from H and hydrocarbyl;and X, Y, and Z are independently selected from O and S.
 23. Theinvention according to claim 23 wherein the antioxidant is of theformula


24. The invention according to any one of claims 2 to 22 wherein thephosphorus-containing antioxidant is a compound of Formula II:

wherein R¹, R² and R³ are independently selected from H and hydrocarbyl;and X, Y, and Z are independently selected from O and S.
 25. Theinvention according to claim 24 wherein the antioxidant istridodecylphosphite.
 26. The invention according to any one of claims 1to 25 wherein the deposit inhibiting compound is of Formula IIPolymer-Q-R   (II) wherein Polymer is a polymeric hydrocarbyl group;wherein Q is an optional ring system; and wherein R is a group selectedfrom H and hydrocarbyl.
 27. The invention according to claim 26 whereinif R is a hydrocarbyl group it is free of a carboxylic acid group(—COOH).
 28. The invention according to claim 26 or 27 wherein Qtogether with R contains no greater than 2 nitrogens.
 29. The inventionaccording to claim 26, 27 or 28 wherein when Q together with R contains2 nitrogens each of the nitrogens is a member of a heterocyclic ring.30. The invention according to any one of claims 26 to 29 wherein Qtogether with R contains only 2 nitrogens and wherein each of thenitrogens is a member of a heterocyclic ring.
 31. The inventionaccording to claim 26, 27 or 28 wherein Q together with R contains nogreater than 1 nitrogen.
 32. The invention according to claim 31 whereinQ together with R contains no greater than 1 basic nitrogen.
 33. Theinvention according to any one of claims 26 to 32 wherein if R is ahydrocarbyl group it is free of a hydroxyl group (—OH).
 34. Theinvention according to any one of claims 26 to 33 wherein the optionalring system Q is present.
 35. The invention according to any one ofclaims 26 to 34 wherein Q is substituted, preferably Q is substitutedwith one or more groups selected from ═O and —OH.
 36. The inventionaccording to any one of claims 26 to 35 wherein Q is an aromatic ring.37. The invention according to any one of claims 26 to 36 wherein Q has4 to 10 members, preferably 4 to 6 members, preferably 5 or 6 members.38. The invention according to any one of claims 26 to 37 wherein Q is acarbon ring or a heterocyclic ring containing carbon and one nitrogen.39. The invention according to any one of claims 26 to 38 wherein Q isselected from a ring system of the formula

wherein A is C or N, preferably Q is selected from a ring system of theformula


40. The invention according to any one of claims 26 to 39 whereinPolymer is a hydrocarbyl group having from 10 to 200 carbons.
 41. Theinvention according to any one of claims 26 to 40 wherein Polymer is abranched or straight chain alkyl group, preferably a branched alkylgroup.
 42. The invention according to any one of claims 26 to 41 whereinPolymer is polyisobutene.
 43. The invention according to any one ofclaims 26 to 42 wherein Polymer has a molecular weight of from 700 to2300, preferably 800 to
 1200. 44. The invention according to any one ofthe preceding claims wherein the deposit inhibiting compound is selectedfrom compounds of the formulae

wherein PIB is polyisobutene.
 45. The invention according to claim 44wherein PIB is polyisobutene having a molecular weight of from 1000 to2300.
 46. The invention according to any one of the preceding claimswherein the composition further comprises a metal deactivator.
 47. Theinvention according to claim 46 wherein the metal deactivator isselected from N,N′-disalicylidene 1,2-propanediamine andN,N′-disalicylidene 1,2-cyclohexyldiamine.
 48. The invention accordingto any one of the preceding claims wherein the composition furthercomprises a further antioxidant.
 49. A fuel composition comprising (a) afuel (b) a composition as defined in any one of the preceding claims.50. A fuel composition according to claim 49 wherein the fuel is anaviation fuel.
 51. A fuel composition according to claim 49 or 50wherein the fuel is JP-8 aviation fuel.
 52. Use of a composition asdefined in any one of the preceding claims for (i) the inhibition ofoxidation of a fuel composition comprising the composition and a fuel;and/or (ii) the inhibition of deposit formation in a fuel compositioncomprising the composition and a fuel; and/or (iii) the inhibition ofparticle formation from the oxidation product(s) of a fuel; and/or (iv)the solubilisation of deposits and/or deposit precursors.
 53. A methodas substantially herein before described with reference to any one ofthe Examples.
 54. A composition as substantially herein before describedwith reference to any one of the Examples.
 55. A fuel composition assubstantially herein before described with reference to any one of theExamples.
 56. A use as substantially herein before described withreference to any one of the Examples.